The mediastinum contains a number of important structures which bear a close relationship to each other in this confined space. A tumor of the mediastinum, whether benign or malignant, is a serious matter. Comparatively small benign tumors may cause very severe symptoms. Malignant tumors of thymic origin, although uncommon, occur frequently enough to be of clinical importance.
Thymic neoplasms are difficult to interpret and to classify. The histogenesis of the thymus, especially the origin of the small lymphoid cells, which compose the larger part of the organ, is not clear. The work of Hammar1 and Maximow,2 however, seems to demonstrate that these cells are true lymphocytes. This conclusion is confirmed by the more recent work of Badertscher.3 According to certain investigators (Stöhr,4 and Papenheimer5) the lymphoid cells are epithelial in origin. It is generally agreed that the cells which form the corpuscles of Hassall are